Interferometer utilizing a tunable laser or similar frequency variable wave energy generator

Claim 2

In an interferometer including optic means for receiving wave energy and providing an interference pattern, said optic means including one movable reflective element, the configuration of said interference pattern being determined at least in part by the position of said movable element and being altered by the movement of said element, the improvement comprising: source means for directing a wave energy signal onto said optic means to provide the interference pattern, the configuration of said interference pattern also being determined at least in part by the frequency of said directed wave energy signal and being altered by the variation of the frequency of said wave energy signal; control means responsive to said interference pattern for varying the frequency of said wave energy signal to provide a predetermined pattern configuration; and measuring means for identifying the frequency variation required to provide said predetermined configuration, said frequency variation being proportional to movement of said movable element and thereby identifying the position of said element.

Claim 3

The interferometer of claim 1 in which said control means comprise means for providing a control signal for varying said frequency to maintain one predetermined pattern configuration during movement of said movable element, the amount of frequency variation required to maintain said predetermined configuration being proportional to the magnitude of any movement of said movable element.

Claim 4

The interferometer of claim 2 in which: said source means comprise a laser generator for providing a laser light signa;l; said laser light signal striking said optic means provides an optic fringe interference pattern; and said control means comprise means for automatically varying the frequency of said laser light signal to maintain the fringes of said optical fringe pattern in predetermined fixed locations, the direction of said frequency variation identifying the direction of displacement of said movable reflective movement.

Claim 5

The interferometer of claim 3 wherein: said fringe pattern comprises a regular pattern of alternate light and dark parallel fringes; in the absence of any frequency variation of said laser light signal, said fringes are moved along a dimension perpendicular to their lengthwise dimension by movement of said movable element, the direction of fringe movement along said dimension being determined by the direction of movement of said movable element; and said control means includes: first and second detectors for respectively receiving first and second portions of said pattern and providing first and second output signals having a difference value that is increased by fringe movement in one direction along said dimension and is decreased by fringe movement in the other direction along said dimension; subtracting means for determining the value of the difference between said first and second output signals; and means associated with said laser generator for responding to changes in the value of said difference by varying the frequency of said laser light signal to return the fringes of said pattern to a predetermined position.

Claim 6

The interferometer of claim 4 in which: the width of each detector along a dimension perpendicular to the lengthwise dimension of the received fringes is equal to the width of an odd number of fringes; the value of said first and second output signals is determined respectively by the light intensity Of the pattern portion received by said first and second detectors; one edge of said first detector that is parallel to said fringes is aligned with a portion of said pattern that is spaced an odd number of fringes from the portion of said pattern aligned with a corresponding edge of said second detector, said alignment causing fringe movement in one direction to increase the value of said first output signal and to decrease the value of said second output signal to thereby increase the value of said difference signal, and causing fringe movement in an opposite direction to decrease the value of said first output signal and to increase the value of said second output signal to thereby decrease the value of said difference signal.

Claim 7

The interferometer of claim 5 in which: said detectors provide equal value output signals when said corresponding edges of said detectors are aligned with the centers of different fringes; and said means for responding to changes in the value of said difference signal comprise means for responding to any non-zero value difference signal and altering the frequency of said laser light signal to provide a zero value difference signal, said responding means increasing the frequency of said laser light signal in response to a difference signal having a first polarity, and decreasing the frequency of said laser light signal in response to a difference signal having an opposite polarity.

Claim 8

The interferometer of claim 4 further including apparatus for simplifying and increasing the accuracy of the alignment between said detectors and said interference pattern to thereby increase the accuracy of the measurements obtained comprising: means for magnifying said interference pattern to increase the widths of said fringes; and slit means for providing spaced images of said magnified interference pattern and for projecting an image of one portion of said magnified interference pattern onto said first detector and an image of a second portion of said magnified interference pattern onto said second detector.

Claim 9

The interferometer of claim 3 in which: the interferometer includes a settable stop to facilitate the rapid positioning of said movable element in a reference position; different fringe patterns having different known proportional relationships between the frequency variation required to and maintain the fringes of the pattern in a predetermined fixed position and the movement of said movable element are obtained by directing different frequency laser light signals onto said optic means with said movable element in said reference position; and said control means include manual control means for overriding said automatic control means and altering the frequency of said laser light signal to provide a pattern having a preselected relationship between frequency variation and displacement of said movable element from said reference position.